The present invention relates to a multiplexing method and apparatus, demultiplexing method and apparatus, access network system, subscriber multiplexing/demultiplexing apparatus, and protocol termination apparatus, which multiplex PPP packets on the basis of MAC addresses and the like, demultiplex the packets on the basis of IP addresses, and simplify an arrangement required for PPP processing by using these multiplexing and demultiplexing processes.
Conventionally, in the Internet, prior to data communication upon forming a communication path between two terminals connected to the Internet, the terminals must be connected to a backbone network through an access network. For this connection, the Point-to-Point Protocol (PPP) is used.
An outline of PPP in an access network will be described first.
In connection to the Internet, each subscriber must terminate PPP for transferring an IP (Internet Protocol) packet in response to an Internet access request. PPP serves to perform authentication, accounting, service management system (SMS) operation, subscriber-specific band allocation, and the like. Any subscriber who is not authenticated/registered cannot form a link itself, and hence can neither transfer data nor receive an IP address itself. Accounting corresponds to a connection time.
PPP is also used in an Internet backbone network. Unlike PPP used in the access network, this PPP serves to, for example, determine a maximum packet length: MTU (Maximum Transfer Unit) size of packets to be exchanged between the backbone network and the access network.
In order to transmit IP data to the backbone network through the access network connected to the backbone network, PPP termination must be performed in each access network. Conventionally, PPP termination is performed at an entrance to an ISP (Internet Service Provider). PPP termination itself has been handled in the conventional access network systems by installing dedicated units (FIG. 19).
The conventional access network system shown in FIG. 19 is comprised of an ATU (Address Transformation Unit)-R 20l, DSLAM (Digital Subscriber Line Access Multiplexer) 30m, ATM SW (Asynchronous Transfer Mode Switch) 40n, and PPP termination apparatus 501. A PC (Personal Computer) 10k is connected to the ATU-R 20l. Note that l of 20l suffixed to ATU-R indicates that there are 1 to P ATU-Rs, m of 30m suffixed to DSLAM indicates that there are 1 to Q DSLAMs, and n of 40n suffixed to ATM SW indicates that there are 1 to R ATM SWs. Reference numeral 4101 denotes an ADSL (Asynchronous Digital Subscriber Line)/VDSL (Very high speed Digital Subscriber Line); 5101, an ATM OC-3c interface; and 6101, an ATM OC-12c interface.
PPP is a protocol for supporting data transfer using a multiprotocol through a communication path between the ATU-R 20l and PPP termination apparatus 50l of the access network system. When PPP processing starts, an LCP (Link Control Protocol) packet of the PPP control packets shown in FIG. 22 is transmitted as a PPP packet transmitted from the ATU-R 20l to the PPP termination apparatus 50l. Whether a given packet is an LCP packet is determined depending on whether the value in the protocol field in the PPP packet is c021. A link is established on the basis of this LCP packet. A user is authenticated concerning the established link.
An NCP (Network Control Protocol) packet is then transmitted, and IP address distribution processing and the like for data transfer to an upper layer are performed on the basis of this NCP packet. Whether a given packet is an NCP packet is determined depending on whether the value in the protocol field in the PPP packet is 8021.
Transfer of an IP packet in which user packet data is inserted is started on the basis of the IP address distributed to the established and authenticated link afterward. The above description is based on the IETF (Internet Engineering Task Force) Documents RFC 1161/1162/1332.
As a frame format used for PPP processing, an HDLC (High Data Link Control Procedure) frame configuration is used. A 32-bit protocol field is added first to the payload of this frame configuration, and then an IP packet is inserted as packet data in the configuration, thereby forming an overall PPP packet.
The above link establishment processing will be described in detail to some extent.
A link protocol for performing link establishment processing before transmission of an IP packet is subordinate to the IP layer (FIG. 20).
As shown in FIG. 22, in link establishment processing, when an Internet access request is generated, control on the link unusing phase advances to the link establishment phase and moves to the authentication phase. The processing so far corresponds to LCP setting in FIG. 23.
When the processing in the authentication phase is properly performed, control is transferred to the NCP phase to perform the above IP address distribution processing and the like. With this operation, a link is established. This processing corresponds to NCP setting in FIG. 23.
After this link establishment processing, transfer of the above IP packet is started. The IP packet is contained in a PPP packet, and the resultant PPP packet is transmitted. With this operation, the IP packet is transmitted. Whether the PPP packet is a PPP data packet is determined depending on whether the value in the protocol field is 0021.
As described above, in both link establishment and IP packet transmission, each PPP packet to be transmitted is created upon addition of a PPP header thereto on the PPP layer of the ATU-R 20l. In addition, this packet is formed into an ATM cell on the AAL5 (ATM Adaptation Layer Type 5) layer and transmitted to the DSLAM 30m through the PHY layer (FIG. 20).
The DSLAM 30m which receives the ATM cell also performs predetermined processing, on the ATML5 layer, for the ATM cell input through the PHY layer. Similar processing is performed in the ATM SW 40n and PPP termination apparatus 50l (FIG. 20).
If, therefore, an overall access network system is formed by using the AAL5 layer (FIG. 20), since the PPP frame whose ATM cell has been subjected to frame header addition processing (PPP Encapsulation) is transmitted, SAR (Segmentation and Reassembly Sublayer) on the AAL5 layer must be performed first to terminate PPP. With this SAR processing, an original PPP frame is reassembled or processing for link establishment is performed by the CPU of the PPP termination apparatus 50l. After link establishment, the subscriber can transfer the IP packet to a backbone network 60l. 
The following problems, however, arise in the prior art described above.
In the prior art, as described above, an apparatus (the PPP termination apparatus 50l in FIG. 19) which discriminates each subscriber who tries to access the Internet and has a function for ATM processing must be installed at an entrance to the backbone network 60l. Such an apparatus must be added every time the number of subscribers increases. In addition, the PPP termination apparatus 50l is often installed near the backbone network 60l to which packets from many subscribers are sent upon multiplexing.
According to the access network system like the one shown in FIG. 19, since the overall access network system is formed by using the AAL5 layer, the overall system inevitably becomes complicated.
As the number of subscribers who access the Internet increases, an apparatus for performing PPP processing as processing indispensable to connection of the subscribers to the backbone network of the Internet must be added. Such an apparatus may be installed in a place as near to the subscribers as possible, i.e., in an apparatus for providing Internet services (e.g., the ATM SW 40n in FIG. 19). In this case, it is required to avoid complication of PPP, complication of its system, complication of a management system for the system, and the like.